The invention relates generally to optical analytical measurements of chemical species and more particularly to fiber optic chemical sensors.
Research and development of sensors for the detection and quantification of particular chemical species or classes of chemical compounds is a fast growing technical field. Yet for all the effort being expended, the development is very much fragmented. Each physical and chemical property to be measured becomes an independent special project because there is no common ground which forms a basic foundation for sensor design. A variety of different types of sensors have been tried, including fiber optic chemical sensors (FOCS), CHEMFETs, piezoelectric crystals, and semi-conductors. Each sensor requires a different chemistry (or chemical composition) and different sensor design for each specific measurement to be made. Thus each new target material initiates a new research and development effort. Accordingly it is highly desired to provide a basic approach to sensor design which can be utilized for a wide variety of applications by the adoption of a single principle.
Typical fiber optic sensors are illustrated by U.S. Pat. Nos. 4,492,121 to Lehto and 4,542,987 to Hirschfeld in which a fluorescent material is attached to the end of a fiber through which an excitation signal and the resulting response signal are transmitted. U.S. Pat. No. 4,523,092 to Nelson illustrates a similar arrangement in which a series of different absorber materials are mounted to the end of a fiber.
U.S. Pat. No. 4,592,664 to Bijlenga shows a device having a luminescent material at the end of a fiber, including an embodiment in which the luminescent sensor material is the core of a light guide. U.S. Pat. No. 4,040,749 to David shows a waveguide having a liquid crystal material on its surface which is sensitive to organic vapor to change the light transmitting capability of the waveguide. U.S. Pat. No. 4,443,700 to Macedo shows an optical waveguide which is deformed to change the transmission of different modes in the waveguide.
U.S. Pat. No. 4,399,099 to Buckles shows a fiber-sheath element for quantitative analysis of an analyte species in a fluid with a reactive species. The device has a core which is transmissive to electromagnetic energy, and which is provided with one or more permeable or semipermeable sheaths. Analyte which penetrates the fiber-sheath element reduces or modifies energy transmission by the element in a cumulative manner.
In place of these case by case approaches, it is desired to produce a type of sensor which can be made very small in size, which is highly stable and rugged, which has a wide selection of component materials, which is non-reactive, which has high sensitivity, which provides a simplified measurement methodology, which can be made very specific to any of a wide range of target species, which has a long lifetime, which has selectable thermal properties, which has selectable transmission properties and which is very low cost. The sensor technology should be applicable to detection of a wide variety of chemical species as in process control and monitoring, pollution and environmetal monitoring, and leak detection, and a wide range of biological species as in in vivo and in vitro medical diagnostics, pharmaceutical tests and measurement of drug usage.
Accordingly, it is an object of the invention to provide a general fiber optical chemical sensor design which can be adapted to the measurement of any selected species merely by suitable choice of materials.
It is also an object of the invention to provide a new approach to fiber optic chemical sensor design using the inherent transmission properties of an optical fiber as the basis for detection of a selected species.
It is another object of the invention to provide a custom fiber optic which inherently performs the desired measurement by virtue of its being a fiber optic by proper choice of the materials forming the fiber optic.
It is a further object of the invention to provide a fiber optic chemical sensor which is simple to construct, can be made from an unlimited number of materials, can be made for a wide variety of target species, is extremely easy to operate, and which is very low cost.